1. Field
One or more example embodiments relate to semiconductor devices. For example, one or more example embodiments provide thin film transistors (TFTs), semiconductor devices including one or more thin film transistors (TFTs) and methods of manufacturing the same.
2. Description of the Related Art
Thin film transistors (TFTs) are used as switching devices and driving devices in flat display devices such as liquid crystal display devices (LCDs) and organic light emitting display devices (OLEDs). The performance of a TFT is affected by the material and state of a channel layer through which charge carriers travel.
Generally, a conventional or related art flat display device includes amorphous silicon TFTs or polycrystal silicon TFTs. Amorphous silicon TFTs have channel layers formed of amorphous silicon, whereas polycrystal silicon TFTs have channel layers formed-of polysilicon.
The charge mobility of an amorphous silicon TFT is about 0.5 cm2/Vs, which is relatively low. Thus, it is relatively difficult to increase the operating speed of such related art flat display devices. Moreover, amorphous silicon TFTs generally have a bottom gate structure. In a bottom gate structure, portions of the source and drain overlap a portion of the gate. As a result, parasitic capacitance increases, thereby reducing the operating speed of the TFT. But, these overlapped portions are required, and thus, it is relatively difficult to scale-down devices using bottom-gate TFTs.
Crystallization, impurities injection, and activation are required to manufacture a polycrystal silicon TFT. Accordingly, the manufacturing process is more complicated and manufacturing costs are higher than an amorphous silicon TFT. In addition, because the size of crystalline particles of a polycrystal silicon layer is irregular, image quality deteriorates display device size increases. Thus, a polycrystal silicon TFT is restrictively used in smaller-sized display devices.